When it's working correctly just a light tap on the brake lever will be responsive, and it will then return to let the wheel spin freely, so i'd say you do still have a a bit of seizing going on.
If you brake when the bike's stationary then you'll always get a very minimal bit of friction but it shouldn't sound like it's rubbing or grating.
Don't get pads that are too harsh for the rear as they can wear the discs down much quicker.
I think i used SBS ceramic pads last time on my bike, rather than organic, to minimise the dust output, which is a main cause of the pots sticking.
Once you've got the rear caliper working properly it's always worth a quick service every 6 months, pads out, gently push the pots out, and clean up with a toothbrush and brake cleaner, then smear red rubber grease on the exposed outer parts of the pots, and it will keep them in good shape for much longer.
Everyone else is going to tell you to upgrade the caliper with a 1000 version, although i've never felt the need personally, but each to their own
i s'pose. 
